The prospective cohort study involved a review of data for nearly 26,000 men, with the findings released on-line in April, ahead of print in the journal this month.

Researchers suggested that Viagra’s active ingredient, sildenafil citrate, appears to lower levels of a cancer-fighting protein called PDE5A, which could potentially increase the invasiveness of melanoma cancer cells. They found no evidence of increases in the risks of other forms of skin cancer.

Since the release of the findings, several product liability law firms have announced that they are now reviewing potential Viagra melanoma lawsuits on behalf of former users of the drug who have been diagnosed with this serious, and potentially deadly, form of skin cancer.

Viagra has been on the market since 1998, when it was approved by the FDA for the treatment of erectile dysfunction. In 2012, the blockbuster drug raked in $2 billion in sales for Pfizer, and the findings of this study have raised questions about how the drug maker failed to detect and warn users about the potential risk of melanoma from Viagra.